The present invention relates to image display devices having a plurality of electron beams each of which scans a different portion of the display, and more particularly to a beam collector which collects and senses the beam current. The beam current information is processed and used to adjust the uniformity characteristics of the electron beams to obtain uniform brightness across the entire screen of the display device.
Beam collectors, such as the so-called "Faraday Cage"-type, designed so that the total current is collected and secondary electrons which are generated are not permitted to escape to other tube elements, are well known in the power tube art. A high power beam tube utilizing a "Faraday Cage"-type beam collector is described in U.S. Pat. No. 3,453,482 entitled "Efficient High Power Beam Tube Employing a Fly-Trap Beam Collector Having a Focus Electrode Structure at the Mouth Thereof", issued on July 1, 1969, to D. H. Preist. One of the problems encountered with such a collector is that complex and costly focusing electrode structure at the mouth of the collector is required for focusing the beam in the decelerating space preceding the mouth of the collector to maintain laminar flow of the electrons in the beam decelerating region. Such focusing structure prevents the setting up of excessive space charge depressions in the deceleration region which would inhibit collection of the total beam current. For such collectors to be practical in display devices, they should utilize as much of the existing device structure as possible to focus the beam while achieving substantially total collection of the electron beam, and either total collection or suppression of secondary and scattered electrons generated by the impingement of the electron beam onto the collector.
U.S. Pat. No. 4,126,814 of Frank J. Marlowe, filed Dec. 9, 1976, entitled "Electron Gun Control System", and U.S. Pat. No. 4,121,137 of Thomas L. Credelle issued Oct. 17, 1978, entitled "System for Achieving Image Uniformity in Display Devices" disclose systems which include collecting the electron beams and sensing their current magnitudes. The Marlowe application does not detail the structure of the collector. The Credelle patent states only that the collectors are U-shaped electrodes located between the focusing guide at the end of the channels.
The present invention is directed to a simple collector structure within the guide, which utilizes existing display device elements modified to provide high collection efficiency and to prevent the escape of secondary and scattered electrons to other tube elements.